The embodiments herein generally relate to methods and systems for monitoring bearings and more particularly to air cycle machines with bearing failure detection systems and associated methods.
Hydrodynamic fluid film journal bearings, also called journal air bearings or foil bearings, can be used to provide support to rotatable components such as shafts. A typical journal bearing may include a journal sleeve, a bump foil, an intermediate foil, and a top foil. The bump foil, the intermediate foil, and the top foil are wrapped inside the journal sleeve in a substantially cylindrical shape, and the foils are positioned between the journal sleeve and the rotatable component. Each foil has an end that is engaged to the journal sleeve, and can have another end that is free, i.e., not engaged to the journal sleeve. During operation, rotation of the rotatable component causes a working fluid to form a cushion (often referred to as an “air bearing”) that supports the rotatable component with little or no direct contact between the rotatable component and the foils of the bearing. Journal bearings provide fluid cushions for radial loads.
Similarly, hydrodynamic fluid film thrust bearings generate a lubricating non-linear air film between a portion of a rotating shaft or other rotatable component and the bearing. One typical bearing arrangement utilizes welded subassemblies. A top subassembly includes an annular main plate having multiple arcuate, corrugated foils welded to the main plate. A corresponding number of arcuate top foils are supported by bump foils. A bottom subassembly includes another annular main plate having multiple arcuate bump foils welded to the main plate. Thus, during operation, rotation of the rotatable component or shaft causes a working fluid to form in and around the corrugated foils to provide an air bearing. The bump foils provide a desired spring rate to cushion the rotatable component as the shaft moves axially. Thus, thrust bearings provide fluid cushions for axial loads.
During operation, the bearings may be rotated at high speeds which results in heat generation. The heat can lead to failure of the bearings by compromising the structural integrity of the components of the bearings. To reduce the risk of failure of the bearings, cooling air is conveyed and passed over bearing surfaces to remove the heat from the bearing.